一氧化氮對東方果實蠅視網膜色素顆粒移動之調控

Abstract

一氧化氮(nitric oxide, NO)為一種半衰期短暫的不穩定氣體分子。在生物體內由一氧化氮合成酶(nitric oxide synthase, NOS)產生，作用於標的細胞內的水溶性鳥苷酸環化酶(soluble guanylyl cyclase, sGC)，以提升細胞內cyclic GMP的含量。NO在昆蟲的中樞神經系統，被學界推測與嗅覺及視覺的形成過程有關，然而NO在昆蟲視覺系統真正的生理功能及作用機制仍有待證實。本研究以NADPH-diaphorase標定東方果實蠅(Bactrocera dorsalis)複眼中的NOS。在初級色素細胞及基底膜相鄰細胞標定出具有活性的NOS。而此兩處的細胞，相較於視官柱體(rhabdome)，含有較多的色素存在。為了驗證NO在此是否與昆蟲視網膜色素的調控有關，以NO生成劑(GSNO)及NO清除劑(C-PTIO)注入東方果實蠅視網膜內，觀察光適應時複眼偽瞳孔(pseudopupil)光影因視網膜細胞內色素顆粒移動所造成的變化。以GSNO處理的視網膜，偽瞳孔光影亮度減弱，在光刺激下視網膜仍保持暗適應的狀態；而對照組維持正常，表示NO的確可影響視網膜細胞內色素顆粒的移動。由本研究的結果推論，NO可由在東方果實蠅的視網膜產生，並且藉由調整色素顆粒的移動而改變其視網膜對光暗的適應狀態。

Nitric oxide (NO) is an unstable gas molecular with short half-life. In organism, NO is produced by nitric oxide synthase (NOS), affects on the soluble guanylyl cyclase (sGC) of target cells, and lead to the increase of cyclic GMP level. In insect central nervous system, NO is supposed to have some physiological functions related to the olfaction and vision. However, the real function and mechanism of NO still need to be proved. In this study, NADPH-diaphorase was used to detect the expression of NOS in the compound eye of oriental fruit fly (Bactrocera dorsalis). The existence of NOS in the primary pigment cell and around the basement membrane was observed. Compare with the rhabdome, these two areas contain more pigments. To verify the relationship between NO and the pigments of insect retinula, the NO donor (GSNO) and the NO scavenger (C-PTIO) were injected into the retinula, and to observe the pseudopupil reflection caused by the migration of the pigment granules in light-adapted retinula cells. The pseudopupil reflection decreased in GSNO treatment group, and the retinula was kept in dark-adaptation with light stimulation, indicating that NO control the pigment granule migration in the retinula cells. According to these results, it is concluded that NO can be produced from the retinula of oriental fruit fly and control the light/dark-adaptation of retinula by regulating the migration of the pigment granules.